A tourbillon mechanism is a device designed to average the running deviation of the positions of the balance of a timepiece. To that end, a tourbillon mechanism comprises a support (for example, a cage in the case of the traditional tourbillon) pivotally mounted on the frame, which is in general an assembly formed by a bridge and a plate and, pivotally mounted on this support, a sprung balance and an escapement comprising in particular an escapement wheel provided with a gear and a pinion. The support comprises a gear kinematically connected to the going train of the timepiece, in general to the third wheel, a toothed gear, mounted fixed on the frame, meshes with the escapement pinion. In this way, each time the balance is in position to receive a driving impulse from the escapement, the torque applied by the third wheel on the gearing causes the support to rotate slightly, the impulse at the balance being given by the escapement, whose wheel rotates by meshing of its pinion with the toothed wheel. The wheels and pinions are generally arranged and numbered such that the tourbillon performs one revolution per minute. Thus, when the timepiece is positioned vertically, the position of the dead-point of the balance performs one revolution per minute, which averages the running deviations in the vertical positions. However, the deviation between horizontal and vertical positions remains.
Various solutions have been proposed to offset this drawback.
For example, a tri-axial tourbillon is known, described in application EP 1,574,916, comprising a cage containing the balance and the escapement rotating according to an axis, the cage being mounted in a second cage so as to be able to rotate around another axis, the second cage in turn being rotatably mounted in a third cage rotating around a fixed axis relative to the timepiece, the three axes being perpendicular to one another. The tri-axial tourbillon is driven by a driving gear mounted on the plate of the timepiece, which drives a pinion secured to the third cage, and causes that cage to rotate around its axis, thus setting a pinion in rotation meshing with a crown-wheel fastened on the plate of the timepiece, which rotates the cage around its axis, the second cage setting the first cage in rotation around its axis by means of a crown-wheel and the seconds pinion secured to the third cage, and thus transmitting the energy from the driving wheel to the ensemble formed by the escapement pinion, the escapement wheel and the balance placed in the first cage.
Such a mechanism has the drawback of being bulky and not aesthetically pleasing due to the presence of several toothed crowns, appearing in particular on the dial side.
Also known is publication WO 2005/071498, which describes a tri-axial tourbillon having three axes perpendicular to one another. The tourbillon is pivoted radially using a device located at the periphery of its outer cage. Such a mechanism has a low impact resistance and is therefore very fragile.
Also known is the tri-axial tourbillon described in the publication “The first triple tourbillon” by Richard Good, F.B.H.I., Horological Journal, April 1983, pages 15-19, said tourbillon comprising three axes perpendicular to one another. The construction conceived by Richard Good nevertheless requires a major cantilever relative to the horizontal axis of rotation of the mechanism, which causes a non-negligible moment of inertia.
One solution to resolve this problem was proposed by Thomas Prescher in his Triple Axis Tourbillon work inspired by patent CH 696,450. This solution consists of using a counterweight to offset the cantilever. However, the counterweight is driven by the cages, which results in creating an additional torque that the system must overcome.
The known tri-axial tourbillon mechanisms therefore have elements that are harmful and counter to the expected characteristics of a tourbillon, namely having the lightest possible system in order to have as limited an inertia is possible, as well as good visibility of the latter.
One aim of the present invention is therefore to offset these drawbacks by proposing a timepiece comprising a tourbillon mechanism making it possible to decrease the moment of inertia of the system.
Another aim of the present invention is to propose a timepiece comprising a robust tourbillon mechanism, having a reduced bulk and improved aesthetic appearance.